The permutation of n things taken r at a time, nPr,
is calculated as follows. For 5P3 enter
5
and press three times to select PRB.
Then, select nPr by pressing . Enter the value of r,
which is 3 and press .

The combination of n things taken r at a time, nCr,
is calculated as follows. For 6C4 enter
6
and press three times to select PRB.
Then, select nCr by pressing . Enter the value of r,
which is 4 and press .